Bug 25131: (QA follow-up) Move test for needs_install outside the plugin

Bug 25131: (QA follow-up) Move test for needs_install outside the plugin

This follow-up patch moves the check outside the register routine. The
Mojo plugin won't be loaded unless there's no need to install.

As the original tests rely on V1.pm to be able to load the plugin, they
are still valid, and they should still pass as there's no behaviour
change.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>